Short range radio networks having a master radio device which subsequently registers or associates slave radio devices with itself to form a master/slave piconet are generating much interest. The interoperability of such master/slave devices (or network nodes) depends on each device having a predetermined and standardised radio protocol, such as those defined in the 802 family of radio standards adopted by the IEEE. A well-known example of such a protocol is the Bluetooth™ protocol. Another protocol in development at the time of this patent application is that being developed by the ZigBee Alliance group of companies (www.zigbee.org). The main aims of the ZigBee Alliance are to define a protocol and radio stack suitable for low data rate, low power applications such that radio devices incorporating the ZigBee standard are of low cost and interoperable. It is hoped that such low cost self-configuring radio device piconets will open up many home consumer and industrial control markets, for example in heating and lighting applications. The ZigBee alliance group of companies are aiming to produce radio devices with a target cost of less than $2 at the time of writing, with such devices having relatively simple microcontrollers acting as a microprocessor and a limited amount of on-board memory available.
However, a ZigBee radio piconet comprising a master node and associated slave nodes has, at the time of making this application, limited radio coverage related directly to the radio broadcast range of the master node which is estimated to be in the region of a few tens of meters for a ZigBee piconet communicating in one of the 16 channels defined in the 2.4 GHz ISM band. Another shortcoming exists in that no scheme for routing messages from one ZigBee piconet to another has been defined, and known ad-hoc mobile network routing methodologies typically require significant resource capabilities to be available in each node, to store for example forwarding/route information which must be inserted into a message en route, such information identifying intermediary and destination node addresses (each address being typically a unique six or eight byte number).
It is therefore an object of the present invention to mitigate the above shortcomings.